Add tree exercises

notes-and-examples/2026.05.27/invert_tree.py

@@ -0,0 +1,40 @@
+# Tree example:
+#       10
+#      /  \
+#     5   15
+#    / \    \
+#   3   7   20
+
+
+class Node:
+    def __init__(self, value, left=None, right=None):
+        self.value = value
+        self.left: Node | None = left
+        self.right: Node | None = right
+
+
+root_node = Node(10)
+root_node.left = Node(5)
+root_node.left.left = Node(3)
+root_node.left.right = Node(7)
+root_node.right = Node(15)
+root_node.right.right = Node(20)
+
+
+def invert_tree(root: Node | None):
+    if root is None:
+        return
+
+    invert_tree(root.left)
+    invert_tree(root.right)
+
+    root.left, root.right = root.right, root.left
+
+
+invert_tree(root_node)
+
+print(root_node.left.value)
+print(root_node.right.value)
+print(root_node.left.left.value)
+print(root_node.right.right.value)
+print(root_node.right.left.value)